水压–应力耦合作用下砂岩应力松弛特性试验研究

Experimental study of stress relaxation characteristics of sandstone under stress and pore-water pressure coupling

基于三维数字图像相关技术,采用可视化三轴压缩伺服控制试验系统,开展孔隙水压–应力耦合作用下砂岩应力松弛特性试验研究。结果表明:(1)径向应变场中局部微裂纹损伤发育并相互贯通是引起脆性岩石应力松弛时效失稳破坏的主控因素。(2)松弛应力水平位于岩石微裂纹稳定发育和微裂纹不稳定发育阶段时,孔隙水压的增加,能显著提高岩石的应力松弛量和径向应变变化量,缩短岩石时效破坏寿命。(3)松弛破坏试样应力–时间曲线和径向应变–时间曲线呈“阶梯式”变化趋势,及两者的速率–时间曲线呈现“漏斗形”演化趋势,其实质均反映了岩石应力松弛过程中微裂纹损伤发育扩展和相互贯通。(4)松弛破坏试样破裂面裂纹发育以沿晶裂纹为主,且相互之间汇集、贯通,胶结基质破碎严重,胶结结构丧失,脆性岩石应力松弛时效破坏实质是受裂纹发育扩展所控制。

Based on three-dimensional digital image correlation technology and adopting a transparent triaxial compression servo-control system,the stress relaxation characteristics of sandstone under the coupling action of pore-water pressure and stress are studied.The temporal and spatial evolution of the strain field in rock surfaces,the stress relaxation curve and micro-morphology of fracture surfaces are analyzed.The results show that:(1)The development and interpenetration of local micro-cracks in the radial strain field are the main controlling factor that causes the failure of brittle rock during stress relaxation.(2)When the relaxation stress level is at the stages of stable and unstable development of micro-cracks inside the rock,the increase of the pore-water pressure can significantly increase the stress relaxation variation and the radial strain change,and shorten the aging failure life of the rock.(3)Both the stress-time curve and the radial strain-time curve of the relaxation failure specimen show a“stepped”trend,and their rate-time curves present a“funnel-shaped”evolution trend,which essentially reflects the development,propagation and interconnection of micro-cracks during the process of stress relaxation.(4)The crack development on the fracture surface of the relaxation failure sample is dominated by intergranular cracks,which converge and connect with each other.The cemented matrix is seriously broken and the cemented structure is lost.The essence of stress relaxation failure of brittle rock is controlled by crack development and propagation.